JP2004511581A - Aqueous black enamel composition for glass substrates - Google Patents

Abstract

The present invention relates to 20-40% by weight of a water-soluble sodium silicate and / or potassium silicate; an amount of a water-soluble base sufficient to bring the pH of the composition to at least 10.5; 10 to 40% by weight of a metal oxide selected from the group consisting of copper oxide, iron oxide, cobalt oxide, a mixture of these oxides, and a mixture of at least one of the above oxides and chromium oxide; % Zinc oxide; at least 10% by weight glass frit having a Littleton softening point higher than 700 ° C., for an aqueous black enamel composition designed to be deposited on a glass substrate, especially a glass plate. is there. The invention further relates to a glazing comprising at least one glass sheet, at least one surface of which is at least partially covered by the enamel composition, in particular for automobiles.

Description

[0001]
The present invention relates to an aqueous black enamel composition that can be deposited on a glass substrate and to the resulting enameled substrate, especially enameled glazing.
[0002]
The use of the enamel composition on glass substrates, in particular on glazings for motor vehicles or buildings, to form any kind of coating, for example a decorative, conductive or protective layer or a layer intended to form a mask It is known to
[0003]
These enamel compositions are particularly found in automotive windshields, side windows and rear windows and serve to form a dark, opaque peripheral zone, which is generally solid but may contain holes. This band has two functions. Firstly, it can protect the adhesive beneath the glazing to be retained and form a mask for solar radiation, and more particularly ultraviolet radiation, when attaching the glazing to the body opening by gluing To Second, it improves the appearance of the vehicle by masking electrical or other connecting elements near the boundaries of the inner surface of the glazing, especially as in the case of rear windows.
[0004]
In general, enamel compositions which help to form such zones include glass frit (which must form a glassy matrix) and pigments (especially gray or black pigments, these pigments may form part of the frit). ), As well as powders containing the same. Pigments are most often metal oxides that do not react with the other components of the composition, such as chromium oxide, cobalt oxide, nickel oxide and iron oxide. The medium ensures that the solid particles are properly suspended and allows the enamel to be applied and temporarily adhered to the substrate. Generally, the medium contains an organic solvent, such as pine oil or terpene, mineral oil, diluent and / or resin, or a UV crosslinkable component.
[0005]
The enamel composition is generally deposited on a glass substrate surface by screen printing, spraying, curtain coating or roll coating, and then fixed to the glass. This fixing operation is necessary so that the substrate can be handled, for example for the purpose of bending and / or reinforcing the substrate without risk of damaging the enamel layer. Depending on the medium used, this fixing can be, for example, a drying operation performed by simply heating to a moderate temperature (around 80-150 ° C.), such as to remove organic solvents, or the medium can be crosslinked. The case may consist of a UV curing operation.
[0006]
One of the problems with existing enamel compositions is the presence of solvents, especially organic solvents. Attempts have been made to replace them with water because of the toxicity of some solvents that the user may come into contact with and because of the potential danger to the environment.
[0007]
Water-soluble sodium silicate, water-soluble base, metal oxide powder and glass frit having a melting point below 1300 ° F. (= US Pat. No. 5,518,535), and further zinc oxide (US Pat. No. 5,518,535). No. 5,698,026), or aqueous enamel compositions containing glass particles having a melting point above 1700 ° F. (= 926 ° C.) (US Pat. No. 5,677,064).
[0008]
However, the aqueous compositions mentioned above have disadvantages. With such a composition, it is difficult to obtain a fusible coating that is compatible with the temperature conditions applied during forming the glazing. This is because, at application temperatures generally not exceeding 650 ° C. (temperature of the glass), the enamel tends to show a residual capillary effect due to insufficient sintering. Furthermore, the enamel obtained under bending conditions does not have the expected properties in terms of color. On clear (unpigmented) glass, the enamel formed has a somewhat dark gray shade, and this shade is not chromatically neutral. The absence of chromatic neutrality produces a gray color that tends to red, green, blue or yellow, depending on the type of pigment used. Finally, it is possible to obtain a black enamel on colored glass, but this coloring does not have the desired "strength" (or "depth"). In particular, it has an L ^* value substantially greater than the value defined hereinafter.
[0009]
The present invention provides a novel aqueous enamel composition that can remedy the above disadvantages. The compositions according to the invention can be deposited on glass substrates, show good adhesion to glass after drying (and consequently good scratch resistance), are anti-adhesive at bending temperatures, and After firing, it makes it possible to obtain a black enamel which forms a durable homogeneous coating.
[0010]
Another object of the present invention is an enamel composition which can be deposited on a transparent glass substrate to produce a chromatically neutral black enamel, which composition is further defined in the preceding paragraph. The advantages of the composition are:
[0011]
Another object of the present invention is a glass substrate coated with the above-mentioned enamel composition, in particular enamel-treated glazing, especially laminated glazing for motor vehicles.
[0012]
In the context of the present invention, the term "enamel composition" means the enamel composition before calcining, and it will be understood that this enamel after calcining essentially takes the form of a colored glassy matrix.
[0013]
The term "black enamel" is understood according to the invention to mean an enamel having an L ^* value after calcination of less than or equal to 8, preferably less than or equal to 6.
[0014]
The expression "chromatically neutral black enamel" is understood according to the invention to mean, after firing, an enamel having the following colorimetric coordinates in absolute value:
L ^* ≦ 8; | a ^* | ≦ 1 and | b ^* | ≦ 1,
Preferably, L ^* ≦ 6; | a ^* | ≦ 0.6 and | b ^* | ≦ 0.6.
[0015]
The colorimetric coordinates L ^* , a ^*, and b ^* were defined and proposed in 1931 by CIE (Commission International de l'Eclairage [International Illumination Commission]), and became the subject of CIE official recommendations in 1976 (International Illumination). Communications, Colorimetry-Official Recommendations-CIE Publication No. 15-2, Vienna, 1986). The above colorimetric coordinates, in reflected light, using a Minolta CM 2002 spectrocolorimeter, viewing angle 10 ° under a light source _{D 65,} measured in specular excluded mode.
[0016]
The term "transparent glass" is used herein to refer to a light transmission coefficient _TL under a light source D ₆₅ of greater than or equal to 90% when measured on a 4 mm thick glass plate having parallel surfaces. It is understood to mean equal glass.
[0017]
According to the present invention, an aqueous black enamel composition that can be deposited on a glass substrate, especially glazing,
20-40% by weight of water-soluble sodium and / or potassium silicate;
An amount of a water-soluble base sufficient to bring the pH of the composition to at least 10.5;
5-25% by weight water;
40 to 60% by weight of a metal oxide selected from the group consisting of copper oxide, iron oxide, cobalt oxide, a mixture of these oxides, and a mixture of at least one of these oxides and chromium oxide;
Less than 10% by weight zinc oxide;
At least 10% by weight of glass frit having a melting point of less than 680 ° C .;
Less than 10% by weight glass frit with a Littleton point higher than 700 ° C.
including.
[0018]
In the context of the present invention, the term "melting point" has the generally accepted meaning in the enamel field, i.e. it means that the glass frit is sufficiently melted and adheres to the deposited glass, The temperature at which a quality layer is formed. This “melting point” is also called “calcination temperature” or “fusion temperature”. It corresponds to the lowest temperature at which the frit exhibits "sufficient" sintering, which is evidenced by the disappearance of the capillary effect. In practice, for those skilled in the art, this consists in determining the temperature at which the frit deposited on the glass substrate must be fired in order to form a layer having pores through which liquid cannot pass. Hereinafter, the expression “glass frit having a melting point of less than 680 ° C.” is referred to as “low melting point frit”.
[0019]
Further according to the present invention, the term "Littleton point" or "(Littleton) softening point" has the accepted meaning in the glass art. "Littleton point" corresponds to the temperature of a glass having a viscosity of ^107.6 poise measured under standard conditions (ASTM C 338). Hereinafter, the expression “glass frit having a Littleton point higher than 700 ° C.” is referred to as “heat-resistant frit”.
[0020]
According to the invention, the water-soluble sodium silicate and / or potassium silicate represents 20 to 40% by weight of the enamel composition, preferably 20 to 30% by weight. The silicate may comprise only one sodium silicate or potassium silicate or a mixture of several sodium and / or potassium silicates. Preferably, the enamel composition does not contain potassium silicate.
[0021]
Water represents 5 to 25% by weight of the composition, preferably 10 to 20% by weight.
[0022]
The water-soluble base according to the invention is used in an amount sufficient to bring the pH of the composition to at least 10.5, preferably greater than 12.5, and more preferably greater than 13.5. To achieve this, any type of known water-soluble base can be used, such as sodium hydroxide or potassium hydroxide. Sodium hydroxide is preferred. A high basicity can in particular ensure that the composition is stored well for a long time.
[0023]
The metal oxide represents 40 to 60% by weight of the composition according to the invention, preferably 50 to 60% by weight. The metal oxide is selected from the group consisting of copper oxide, iron oxide, cobalt oxide, a mixture of these oxides, and a mixture of at least one of these oxides and chromium oxide, which is desirable for the enamel. To give a black color. Preferably, the metal oxide is selected from a mixture of chromium oxide and copper oxide and / or iron oxide.
[0024]
In one advantageous embodiment, the metal oxide is copper chromite (Cr ₂ O ₃ .CuO), iron chromite (Cr ₂ O ₃ ), especially when the substrate to be coated is made of transparent glass. FeO) or a mixture of these chromates (preferably containing at least 50% by weight of copper chromite). Particularly preferably, the metal oxide consists entirely of copper chromite.
[0025]
The metal oxide is generally in finely divided form and has an average particle size of less than 7 μm, preferably 5 to 7 μm, advantageously less than 5 μm.
[0026]
Zinc oxide represents less than 10% by weight of the composition according to the invention, preferably 1 to 6% by weight, more preferably 4 to 6% by weight. Zinc oxide serves as an accelerator for the components of the composition to adhere to the glass. This has the effect of improving the compatibility between the enamel and the glass, especially by reducing the difference in the expansion coefficient between the enamel and the glass.
[0027]
The low melting frit represents at least 10%, preferably 10 to 30%, and more preferably 10 to 25% by weight of the composition according to the invention. Examples include bismuth borosilicate glass frit, zinc borosilicate glass frit, and lead borosilicate glass frit (although the latter is undesirable because of the inherent presence of lead in the environment). The glass frit according to the invention can consist of a single frit or a mixture of several frits selected from the aforementioned frit. In particular, if the content of this frit exceeds 20%, it is advantageously a bismuth borosilicate or zinc borosilicate glass frit containing a nucleating species capable of crystallizing the frit. The use of such a frit improves the anti-adhesion of this enamel, especially when bending a pair of glass plates for the purpose of forming a mating glazing, and the transfer of the enamel on the glass surface facing the coating. It is possible to avoid. Bismuth borosilicate glass frit is preferred, especially because it provides greater resistance to chemicals. In a preferred embodiment, especially for the production of laminated glazing, the melting point of the glass frit is below 600C, advantageously between 500 and 600C.
[0028]
In the composition according to the invention, the heat-resistant frit content varies below 10% by weight, preferably from 4 to 10%, more preferably from 0 to 4%. Generally, and preferably, especially with respect to glazing, the composition does not contain a heat-resistant frit. An example is a soda-lime glass frit, for example float glass. The heat resistant frit is generally in the form of particles having an average size of less than 20 μm, preferably 3-15 μm, and more preferably 5-7 μm.
[0029]
In addition to the essential components mentioned above, the compositions according to the invention can contain small amounts (generally less than 1% by weight, preferably less than 0.5% by weight) of surfactants acting as wetting agents with respect to the glass. it can.
[0030]
The compositions according to the invention can also contain low-expansion ceramic frit-type components, in particular those based on zirconium or alumina, for lowering the expansion coefficient (zirconium silicate or alumina silicate). At a rate of 5 to 25%, preferably 10 to 20%).
[0031]
The amount added depends on the composition of the base of the enamel, the composition of the glass, the contour of the edge of the glass, the position of the enamel relative to the edge of the glass and the thickness of the enamel.
[0032]
In particular, if the enamel is deposited on the very edge of the glass, and if the edge is shaped to be rounded, so that a relatively thick enamel of approximately 100 μm or more at the end of the glass is preferred, this addition Will be larger. This is because the high coefficient of expansion of this type of enamel creates detrimental elongational stress in the glass.
[0033]
Because the components that reduce the expansion coefficient are infusible, their particle size is selected to be preferably small, preferably less than 20 μm, so as not to affect the appearance of the enamel, especially its roughness.
[0034]
The composition according to the invention can be produced by simply mixing the various components in a suitable device, for example a ball mill, for a time long enough to obtain a homogeneous mixture. This mixing is generally carried out at room temperature (around 25-30 ° C.). However, a method comprising dissolving the sodium silicate and, if appropriate, potassium silicate in water, preferably with vigorous stirring, and adding the other components of the composition to this solution (the order of addition is Insignificant) is preferred.
[0035]
The resulting mixture is then deposited on a glass substrate. The glass used may belong to any type of glass normally used in the field of glazing for motor vehicles or buildings, for example soda-lime glass (float glass).
[0036]
Any method known in the art can be used to deposit this mixture on the glass, such as screen printing, spraying, curtain coating or roll coating. When using the preferred method of screen printing, suitable equipment may be maintained under humidity control conditions, preferably relative humidity close to 80-85%, as described in US Pat. No. 5,509,964. Recommended.
[0037]
The shape, size and number of coatings on one or more sides of the glass substrate will depend substantially on the intended application. In motor vehicles, at least one type of coating is generally applied to the periphery of the glazing in the form of bands of various widths. However, it is applied with a width sufficient to mask the underlying elements of the glazing (these may be adhesives and / or connecting elements, especially electrical connecting elements, as pointed out above).
[0038]
The thickness of the coating can vary according to the intended use. In the case of the above-mentioned bands, the thickness is generally between 15 and 35 μm, preferably between 20 and 28 μm.
[0039]
Once the substrate has been coated with the composition according to the invention, the substrate is heated to a temperature high enough to remove water and adhere the coating to the glass. However, this temperature is lower than the softening temperature of the substrate, so that deformation of the glass which causes optical defects, which must be avoided when making automotive glazing such as windshields, is prevented. Is done. Generally, heating is performed at a temperature below 500 ° C, preferably at 250 ° C. For this purpose any known means can be used, for example microwave or infrared radiation. If several layers are deposited on the substrate, each layer is preferably dried before depositing the next layer. Preferably, the substrate has only a single enamel layer according to the invention.
[0040]
Firing a glass sheet coated on at least one side, preferably only one side with the enamel composition, if appropriate during a heat treatment involving bending and / or strengthening of the substrate. .
[0041]
The glass substrate is generally heated at a firing temperature of around 560-640 ° C., preferably about 580-600 ° C. (“slight” bending) and 600-620 ° C. (“deep” bending), in a manner known per se. And preferably to reach this temperature in less than about 10 minutes. This bending is performed by gravity or by die, as is particularly the case for glass substrates that are bent in pairs for the production of laminated glazing.
[0042]
The strengthening of the glass substrate, in particular the glass substrate used for monolithic glazing, is generally carried out at a temperature of around 640-680 ° C., for no more than a few minutes, using methods known per se. When bending and strengthening the substrate, the reinforcement can be performed after bending the enameled substrate, and possibly with the same equipment.
[0043]
In one particularly advantageous embodiment, the substrates coated with the composition according to the invention are of various thicknesses (generally 1.6) for producing laminated glazing, in particular laminated glazing for automotive windscreens. To 2.6 mm, preferably 2.1 to 2.6 mm). In this case, the enameled glass sheets are combined with at least one other glass sheet and these sheets are bent. Preferably, the second glass sheet is not enameled and the glass has the same composition as the first glass sheet. Preferably, the thickness of the second glass sheet is in the above-mentioned range, more preferably the same as the first sheet. It is particularly advantageous for the glass sheet during the bending process to be positioned such that the side with the enamel composition constitutes in the final position the second side of the mating glazing (the inner side of the outer plate). Separating the bent glass sheets (separation is easier if there is no sign of bonding) and inserting between them at least one insert film made of a different material, for example an organic material such as polyvinyl butyral, They are then combined using heat and pressure to form a combined glazing.
[0044]
The compositions according to the invention are particularly suitable for coating enamelled glass substrates or glass substrates which have already been coated with one or more enamel layers. The substrate consists of one or more glass sheets and can be reinforced to exhibit improved mechanical strength and heat resistance. Thus, the substrate coated with the enamel according to the invention comprises at least one glass plate, at least part of one surface of which is coated with at least one layer of the enamel having the composition according to the invention.
[0045]
The following examples illustrate, but do not limit, the invention.
[0046]
In an embodiment, the melting point of the low melting point frit is determined by depositing a glass frit (thickness: 15 to 30 μm) on a glass plate (length: 150 mm; width: 60 mm) and forming a suitable temperature gradient (width: about 100 ° C.). In general, two temperature gradients, one varying from 500 to 600 ° C. and the other from 600 to 700 ° C., are sufficient). After cooling to room temperature, a line is drawn with a felt pen on the vitrified resulting layer (from the area of the layer corresponding to the lowest temperature to the area of the layer corresponding to the highest temperature), and by examining the substrate, The point at which the line (corresponding to the penetration of the solvent into the layer) is determined. The temperature associated with the above point corresponds to the melting point of this frit.
[0047]
The Littleton point of the heat-resistant frit is determined under the conditions of the aforementioned ASTM C 338 standard.
[0048]
Example 1
A black enamel composition was prepared by mixing the following parts A and B (by weight percent) at room temperature with stirring (around 100 rpm):
Part A:
Sodium silicate 23
Water 11
Part of sodium hydroxide B in an amount sufficient to bring the pH to 10.5:
Copper chromite 52
Zinc oxide 1
Bismuth borosilicate glass frit (melting point around 600 ° C) 13
[0049]
The enamel composition thus produced was deposited on a transparent glass plate (PLANILUX®; thickness: 2.6 mm) by screen printing in a wetting medium (coating thickness: 25 μm). The plate coated with this composition was heated to 220 ° C. (time: 3 minutes). After cooling, a uniform scratch-resistant coating with an L ^* value of 18 was obtained.
[0050]
The above-mentioned glass plate (large glass plate) on a horizontal bending frame, with the surface coated with the enamel composition facing upwards, and a slight glass made of the same type of glass as the first one, but lacking the enamel composition A second plate (small glass plate) with a small size and a thickness of 2.1 mm was placed on the plate. The assembly was heated to about 610-620 ° C (duration: 8-10 minutes) and then cooled to room temperature. A large glass plate has a thickness with the following colorimetric coordinates: L ^* = 5-6; a ^* ≦ 0.5 and b ^* ≦ 0.5 (these coordinates were measured at 20 points on the enamel layer). Coated with black enamel about 16 μm thick.
[0051]
Example 2
A black enamel composition was prepared by mixing the following parts A and B (by weight percent) at room temperature with stirring (around 100 rpm):
Part A:
Sodium silicate 23
Water 11
Part of sodium hydroxide B in an amount sufficient to bring the pH to 10.5:
Copper chromite 41
Zinc oxide 3
Bismuth borosilicate glass frit (melting point around 600 ° C) 22
[0052]
The enamel composition thus produced was deposited on a transparent glass plate (PLANILUX (registered trademark); thickness: 2.1 mm) by screen printing in a wet medium (coating thickness: 22 μm). The plate coated with this composition was heated to 220 ° C. (time: 3 minutes). After cooling, a uniform scratch-resistant coating with an L ^* value of 15 was obtained.
[0053]
On a horizontal bending frame, the above-mentioned glass plate (large glass plate) was made of the same type of glass as the first, except that the surface coated with the enamel composition was facing upwards and lacked the enamel composition A slightly smaller 2.1 mm thick second plate (small glass plate) was placed. The assembly was heated to about 580-600 ° C (duration: 8-10 minutes) and then cooled to room temperature. The large glass plate has the following colorimetric coordinates (measured under the conditions of Example 1): L ^* = 5-6; about 16 μm thick black enamel with a ^* ≦ 0.5 and b ^* ≦ 0.5 Coated.
[0054]
COMPARATIVE EXAMPLE This example was performed except that the enamel composition was different in one part and that the thickness of the layer deposited by screen printing was 24 μm. Performed under the conditions of Example 1.
[0055]
The composition contained (by weight percent):
Part A:
Sodium silicate 25
Water 15
Part of sodium hydroxide B in an amount sufficient to bring the pH to 10.5:
Copper oxide 25
Bismuth borosilicate glass frit (melting point around 680 ° C) 5
Soda lime float glass frit (Littleton point around 730 ℃) 30
[0056]
After bending, the large glass plate is a yellowish gray with the following colorimetric coordinates (measured under the conditions of Example 1): L ^* = 15; a ^* = 0.8 and b ^* = 1.7. Enamel.
[0057]
In the example according to the present invention, the enameled glass plate obtained after the bending step was easily separated (no attachment points). Furthermore, the enamel heated through the face of the large glass sheet (the second face of the glazing in the final position) must be evenly distributed on the surface of the glass and the small glass in contact with the large glass sheet It was found that there was no trace of enamel on the surface of the plate (third surface).

Claims (18)

20-40% by weight of water-soluble sodium and / or potassium silicate;
An amount of a water-soluble base sufficient to bring the pH of the composition to at least 10.5;
5-25% by weight water;
40 to 60% by weight of a metal oxide selected from the group consisting of copper oxide, iron oxide, cobalt oxide, a mixture of these oxides, and a mixture of at least one of the oxides and chromium oxide;
Less than 10% by weight zinc oxide;
At least 10% by weight of glass frit having a melting point of less than 680 ° C .;
Less than 10% by weight glass frit with a Littleton point higher than 700 ° C.
An aqueous black enamel composition capable of being deposited on a glass substrate, comprising: The composition according to claim 1, wherein the metal oxide is selected from a mixture of chromium oxide and copper oxide and / or iron oxide. 3. The composition according to claim 2, wherein the metal oxide is copper chromite, iron chromite or a mixture of these chromites. 4. The composition according to claim 1, wherein the metal oxide consists entirely of copper chromite. 5. The composition according to claim 1, comprising 50 to 60% by weight of a metal oxide. Composition according to any one of the preceding claims, characterized in that it comprises from 10 to 30% by weight of glass frit having a melting point below 680C. 7. The composition according to claim 1, comprising 20 to 30% by weight of water-soluble sodium and / or potassium silicate. The composition according to claim 1, comprising 10 to 20% by weight of water. 9. The composition according to claim 1, comprising 1 to 6% by weight of zinc oxide. Composition according to any of the preceding claims, characterized in that it comprises between 4 and 10% by weight of glass frit with a Littleton point above 700C. The composition according to claim 1, wherein the melting point of the glass frit is less than 600 ° C. 11. The composition according to claim 11, wherein the melting point is from 500 to 600C. 13. The frit having a melting point below 680 [deg.] C., characterized in that it is a bismuth borosilicate, zinc borosilicate or lead borosilicate glass frit or a mixture of these frit. Composition. 14. The composition according to any one of claims 1 to 13, characterized in that it comprises a component for reducing the expansion coefficient of the zirconium silicate or aluminum silicate type. The composition according to claim 14, characterized in that a component for lowering the expansion coefficient is added in a ratio of 5 to 25%, preferably 10 to 20%. A glass sheet, at least one side of which is at least partially covered by the enamel composition according to any of the preceding claims. 17. A glass sheet according to claim 16, which is coated with the composition according to any of claims 14 and 15, wherein the composition is deposited on the very edges. 16. A laminated glazing comprising at least two glass sheets separated by at least one sheet of organic material, in particular a laminated glazing for a motor vehicle, at least one surface of which is at least one surface. Laminated glazing, especially for motor vehicles, comprising at least one glass sheet at least partially coated with the enamel composition according to paragraph.